Endotracheal tubes are widely used in anesthesia and critical care medicine. In use, endotracheal tubes provide access to the upper airways for controlled, assisted ventilation or spontaneous unassisted ventilation with positive end expiratory pressure.
One of the drawbacks of inserting an endotracheal tube into an upper airway of a patient results in the reduction of the lumen of the airway. One cause by which the lumen is reduced is the inability to use the largest possible endotracheal tube for a given patient without subjecting the patient to increased risks. Generally, it is not advisable to insert the largest possible endotracheal tube in a patient since such an attempt will entail many trials and errors which may take additional time which should be avoided especially in critical care or emergency situations.
In addition, the wall thickness of an endotracheal tube needs to be such to provide sufficient strength so as to be safely handled by the using physician or technician during insertion and to maintain the tube stable after insertion. At present, adult endotracheal tubes range between 7 to 9 millimeters in internal diameter with a total wall thickness ranging between 1.4 and 1.5 millimeters. For newborn endotracheal tubes, the decrease in lumen internal diameter as a result of the required wall thickness amounts to approximately 0.5 millimeters or more.
Any decrease in the lumen due to wall thickness of an endotracheal tube has a profound effect on the airway resistance, since the resistance to air flow is inversely proportional to the fourth power of the radius.
As a result of the deficiencies in prior art endotracheal tubes, a need has developed to provide an endotracheal tube having reduced airway resistance so as to facilitate establishment of artificial airways other than those using mechanical ventilators.
Conventional technology used in the fabrication of blood catheters uses either extrusion or dip coating onto mandrels. Extrusion technology has the advantage of low cost, but has little flexibility. With extrusion, the resulting thin wall catheters are rather stiff and are liable to kink or bend and thus obstruct the inner passageway. The dip coating technique used for currently available catheters and tubes is not reproducible in thin wall gauges and, therefore, wall thickness remain substantial.
Currently used endotracheal tubes (ETT) are well standardized worldwide, and are for the most part manufactured from extruded polyvinyl chloride (PVC). Except for the newborn patient population, standard endotracheal tubes have at their distal end an inflatable cuff for an airway seal with the trachea. In addition, there is a limited use for specialty endotracheal tubes to meet the needs of various applications.
For successful use, it is important to provide a good seal between the outer wall of an endotracheal tube and the trachea into which it is inserted. Conventionally, such a seal is provided by using an inflatable cuff attached to the endotracheal tube. Such inflatable cuffs utilize either low or high pressure fluids to cause them to inflate and thus require additional fluid passageways that are connected to the inflatable cuffs.
Unfortunately, the use of .inflatable cuffs is sometimes injurious to the trachea, causing pressure necrosis, bleeding, fistula formation, etc. Following removal of endotracheal tubes having inflatable cuffs, particularly following long term use, there is a significant potential for scar formation with resultant tracheal stenosis. Because of the above sequelae, the use of inflatable cuffs is frowned on in conjunction with newborns and small children, because such adverse effects oftentimes are far more debilitating were they to occur in patients other than adults.
As a result of the above problems and concerns and design limitations, endotracheal tubes up to size 5 mm do not presently employ inflatable cuffs. As an adverse side effect to this accepted design which lacks a sealing means, there is likely to be a significant air leak that can at times be very troublesome.
The concept of modifying the shape of a standard endotracheal tube in its laryngeal portion was suggested by Hengerer in 1975 for the purpose of reducing grooving in the vocal cords (Hengerer et al, "Injuries to the Neonatal Larynx from Long-term Endotracheal Tube Intubation and Suggested Tube Modification for Prevention", Ann. Otol. Rhinol. Laryngol. 1975;84:764-770). Hengerer proposed changing a 2 cm section of endotracheal tube into a triangular shape for use in newborns. Miller et al have suggested attaching silicone rubber rings onto the most distal portion of the endotracheal tube for the purpose of attaining an airway seal within the trachea (but not with the larynx) (Miller et al, "Tracheal Stenosis Following Prolonged Cuffed Inturbation: Cause and Prevention", Ann. Surg. 1970;174:283-293). These, and other efforts have been stymied by the enormous difficulties to a very complex problem.
Bishop, on reviewing laryngotracheal injury following prolonged tracheal intubation suggested that the ideal shape of the endotracheal tube at the level of the larynx ought to be pentagonal in cross-section (Bishop, "Laryngeal Effects of Prolonged Intubation", Anesth. Analg. 1984;63:335-342); the technology then available made such solution impossible.
While the use of presently available commercial endotracheal tubes is unlikely to have major adverse effects in short term applications, problems encountered in long term orotracheal or nasotracheal intubation have been serious, and have defied solution thus far.
The present invention provides an ultra-thin walled wire reinforced endotracheal tube which provides reduced airway resistance to permit easier breathing by a patient. The ultra-thin walled endotracheal tube comprises a polymer having incorporated therewith a metallic spring material to form a continuous tubing. The combination of the polymer and metallic spring material provides an ultra-thin wall of the tubing which permits the use of an endotracheal tube having similar diameters as prior art tubings but with increased internal diameters and resultant reductions in airway resistance.
The present invention also provides an endotracheal tube design that includes a laryngeal section which has a cross sectional shape that is complementary to the cross sectional shape of a subject's larynx. The laryngeal section is provided with seal means which effectively provide a fluid tight seal between the outer wall of the tube and the trachea.
The present invention further provides a novel sealing means which avoids the use of inflatable cuffs, and which is applicable to endotracheal and similar tubes of all sizes including those having an outside diameter which is less that about 5 mm.